1. Field of the Invention
The present invention relates to an improvement in a dust seal of a linear guide apparatus.
2. Description of the Prior Art
Generally, a linear guide apparatus includes, as shown in FIG. 9, a guide rail 1 extending in the axial direction, and a slider 2 mounted movably on the guide rail 1 straddling the same. The guide rail 1 has axially extending ball rolling grooves 3 formed in both side surfaces, and a slider main body 2A of the slider 2 has ball rolling grooves (not shown) formed in inner surfaces of both side walls so that the ball rolling grooves of the slider main body respectively correspond to the ball rolling grooves 3 of the guide rail 1. Balls are interposed rollably between the opposing pairs of ball rolling grooves of the guide rail 1 and the slider main body 2. The slider 2 is movable through the rolling of the balls on the guide rail 1 in the axial direction. During movement, the balls interposed between the guide rail 1 and the slider 2 roll to an end of the slider main body 2A. In order to move the slider 2 continuously in the axial direction, it is necessary to circulate the balls. To this end, axially extending through holes (not shown) are formed as ball paths in both side walls of the slider main body 2A. Furthermore, end caps 5 are attached to opposite ends of the slider main body 2A. Each of the end caps 5 has a pair of ball circulating paths having a U-shape curve which connects each of the ball rolling grooves to a corresponding through hole to form a ball circulating path.
The guide rail 1 has an axially extending recessed groove 6, formed in the upper surface of the guide rail 1, extending the entire length thereof. Inserting holes 6A for retaining bolts (not shown) are provided to fix the guide rail 1 to a base (not shown). The bolt inserting holes 6A are formed at predetermined intervals in the axial direction of the guide rail 1. On the upper surface of the guide rail 1, ridges extend along both sides of the inserting holes 6A and the recessed groove 6, and the ridges have flat portions 6B.
The end caps 5 are usually provided with dust seals 10 because dust, dirt, and the like (hereinafter referred to as foreign particles) are apt to be deposited on the ball rolling grooves 3 and the recessed groove 6 upon which the slider 2 moves. The result of these foreign particles is a disturbance of the smooth rolling of the balls.
A dust seal 10 as shown in FIGS. 9 and 10 was previously proposed (Japanese Utility Model Laid-Open Publication No. 60-103623) by the applicant of this application. This dust seal 10 includes metallic plate 7 which is fixed by small screws 11 to end face of the end cap 5 with the rear surface of the metallic plate 7 brought into contact with the end face of the end cap 5. The dust seal 10 further includes a rubber member 8 which is bonded to the front surface of the metallic plate 7. The dust seal 10 is formed with an opening 9 formed in the lower central portion to allow the guide rail 1 to pass therethrough, and the dust seal 10 is formed in a substantially inverted U-shape. The inner edge of the metallic plate 7 which defines the opening 9 has a simple straight shape. On the other hand, the inner edge of the rubber member 8 at which the opening 9 is formed has semicircular shaped seal protrusions 8a corresponding to the ball rolling groove 3, and a trapezoidal shaped seal protrusion 8c corresponding to the recessed groove 6 of the guide rail 1.
Lip portions having an acute angle are formed at the tip ends of the seal protrusions 8a and 8c, and slide on the outer surface of the guide rail 1, including the ball rolling grooves 3 and the recessed groove 6, to wipe out the foreign particles deposited thereon thereby achieving a dust seal.
The reference numeral 13 designates a nipple for supplying lubricant to the ball circulating paths.
In such a dust seal, the foreign particles desposited on the upper surface and the side surfaces of the guide rail are removed by the seal member which is formed to match the shape of the cross section of the guide rail. For this reason the following problems are involved.
The openings of the inserting holes 6A in the upper surface of the guide rail are formed to allow bolts to be inserted therein. It is impossible to wipe and remove foreign particles deposited in the recesses of the inserting holes 6A completely utilizing the seal protrusion 8c having a trapezoid shape. As a result, foreign particles which have passed through the seal protrusion 8c are scattered in the inside of the slider 2, where they can easily intrude into the ball circulating paths to impair the dust sealing function.
When the seal lips are pressed against the surface of the guide rail with a large pressure, a difference in surface pressure caused when the seal protrusion 8c passes over the recess of the inserting hole 6A produces a variation in resistance. Thus, the travelling function of the slider 2 is degraded.
Moreover, unless the opening edge of the bolt inserting hole is bevelled satisfactorily, the lip portion of the trapezoid seal protrusion 8c of the dust seal 10 will be caught by the opening edge. Thus, a resistance is caused against the movement of the slider and the life of the dust seal 10 is shortened.